Apparatus for plating small-sized plating-piece

ABSTRACT

An apparatus for plating small-sized plating-pieces has a cathode and a plurality of grooves are formed on the surface of the cathode which is to come into contact with small-sized plating-pieces, so that an electric field can be concentrated onto the vicinities of the grooves. Thus, the electric field can be sufficiently dispersed on the whole cathode.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an apparatus for electroplating a small-sized plating piece such as a small-sized electronic component and more particularly, to an improvement in the structure of a cathode thereof.

[0003] 2. Description of the Related Art

[0004] Outer electrodes provided on the outer surfaces of chip-type small-sized electronic components such as monolithic ceramic capacitors, cylindrical capacitors, stacked varistors, stacked inductors, and other such devices are plated in many cases. For example, Japanese Unexamined Patent Application Publication No. 5-70999 describes the use of a plating apparatus shown in FIG. 6 when the above-described plating is carried out by an electroplating method.

[0005] Referring to FIG. 6, the plating apparatus 1 contains a plating bath which has a plating solution 2. A cathode 4 and an anode 5 each made of a conductor are dipped in the plating solution 2.

[0006] A plurality of small-sized plating pieces (a set of the pieces are schematically shown by the broken line) to be plated are placed in a container 7 for components disposed in the plating solution 2. The plating pieces 6 include a plurality of small-sized electronic components 6 a and also a plurality of media 6 b made of conductors.

[0007] The above-described electrode 4 is arranged so as to define a portion of the bottom of the component-container 7. Thus, the small-sized electronic components 6 a and the media 6 b are placed on the cathode 4 in the plating solution 2.

[0008] The component-container 7 is provided with a vertical shaft 8. The component-container 7 is rotated on the vertical axial line of the vertical shaft 8 so that the plating solution 2 is agitated, and moreover, the agitation-action is exerted on the small-sized electronic components 6 a and the media 6 b, so that the small-sized electronic components 6 a and the media 6 b can evenly contact the cathode 6, respectively.

[0009] To conduct between the cathode 4 and the anode 5 provided in the above-described plating apparatus 1, a predetermined voltage is applied between these electrodes. Thus, plating films are deposited onto the outer electrodes (not shown) of the small-sized electronic components 6 a. That is, the outer electrodes are electroplated as is desired.

[0010] When plating is carried out using the above-described plating apparatus 1, inevitably, a deposit is more or less formed on the surface of the cathode 4. Particularly, the deposit is formed on the cathode 4 in such a large amount that the small-sized electronic components 6 a and the media 6 b cannot contact the cathode 4 very easily and completely.

[0011] Moreover, the surface of the cathode 4 provided in the plating apparatus 1 which is to come into contact with the small-sized electronic components 6 a and the media 6 b is so smooth and flat that the agitation of the small-sized electronic components 6 a and the media 6 b is not disturbed.

[0012] However, when the cathode 4 has a smooth surface as described above, an electric field tends to be concentrated on the edges of the cathode 4 during plating. In some cases, the deposit 9 forms protuberances 10 on the edges of the cathode 4 as shown in FIG. 7.

[0013] The above-described protuberances 10 disturb the agitation of the small-sized electronic components 6 a and the media 6 b, and moreover, cause the deposit to peel off during plating. As a result, in some cases, the deposit 9 adheres as foreign matters to the small-sized electronic components 6 a.

[0014] As described above, the protuberances 10 formed on the deposit 9 disturb the agitation of the small-sized electronic components 6 a and the media 6 b. Thus, when the agitation is disturbed, the state in which the small-sized electronic components 6 a and the media 6 b are prevented from contacting with the cathode 4 occurs very easily and completely. In this state, the deposit is formed in a larger amount, so that the protuberances 10 readily occur. Thus, this process is undesirably repeated.

SUMMARY OF THE INVENTION

[0015] In order to overcome the problems described above, preferred embodiments of the present invention provide a plating apparatus for greatly improving a process for plating a small-sized plating piece.

[0016] According to a preferred embodiment of the present invention, an apparatus for plating a plurality of small-sized plating-pieces includes a plating bath in which a plating solution is contained, and a cathode and an anode made of conductors, which are dipped into the plating solution, respectively, the cathode having concavities formed on the surface thereof which is to contact with the small-sized plating-pieces, wherein a plurality of the small-sized plating-pieces are caused to contact with the cathode in the plating solution, and conduction is carried out between the cathode and the anode, so that plating films are deposited onto the small-sized plating-pieces.

[0017] The concavities may be a plurality of grooves formed on the surface of the cathode which is to contact with the small-sized plating-pieces, may be a plurality of small holes formed on the surface, or may be a chamfer portion formed on the circumferential edge of the surface.

[0018] In the case in which the concavities are grooves, preferably, the grooves are arranged so as to intersect each other.

[0019] Preferably, the apparatus for plating small-sized plating-pieces of a preferred embodiment of the present invention also includes a container for accommodating a plurality of the small-sized plating-pieces in the plating solution, and the cathode is arranged so as to define a portion of the bottom of the container.

[0020] Preferably, the container is arranged to be rotated about a vertical axis thereof

[0021] Preferred embodiments of the present invention can be applied to different types of small-sized plating-pieces, and advantageously, is applied to plating of small-sized electronic components.

[0022] Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 illustrates a plating apparatus according to a first preferred embodiment of the present invention, and is a plan view of a container provided in the plating apparatus;

[0024]FIG. 2A is an enlarged plan view of the portion of the container shown in FIG. 1 in which a cathode is disposed;

[0025]FIG. 2B is a cross-sectional view thereof;

[0026]FIG. 3 illustrates a cathode according to a second preferred embodiment of the present invention, and corresponds to FIG. 2A;

[0027]FIG. 4 illustrates a cathode according to a third preferred embodiment of the present invention, and corresponds to FIG. 2A;

[0028]FIG. 5 illustrates a cathode according to a fourth preferred embodiment of the present invention, and corresponds to FIG. 2A;

[0029]FIG. 6 is a schematic cross-sectional view of a plating apparatus relevant to preferred embodiments of the present invention; and

[0030]FIG. 7 is a cross-sectional view of a container, and illustrates problems to be solved by preferred embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0031]FIG. 6 will be also referred to for illustration of a preferred embodiment of the present invention. Regarding the plating apparatus 1 shown in FIG. 6, one of the novel characteristics of preferred embodiments of the present invention is the structure of the cathode 4.

[0032]FIG. 1 illustrates a first preferred embodiment of the present invention, and is a plan view of a component-container 7.

[0033] Cathodes 4 a are arranged so as to define a portion of the bottom of the component container 7. According to this preferred embodiment, four electrodes 4 a are preferably arranged at intervals of about 90° around a shaft 8.

[0034]FIG. 2B is an enlarged view showing the portion of the component container 7 in which the cathode 4 a is disposed. FIG. 2A is an enlarged plan view of the portion of the component container, and FIG. 2B is a cross-sectional view thereof.

[0035] As shown in FIGS. 2A and 2B, a plurality of grooves 11 are formed on the upper surface of the cathode 4 a, that is, on the surface of the cathode 4 a which is to come into contact with the small-sized electronic components 6 a as the plating-pieces 6 and the media 6 b (see FIG. 6). These grooves 11 form concavities on the upper surface of the cathode 4 a. The widths of the grooves 11 are preferably smaller than the respective sizes of the small-sized electronic components 6 a and the media 6 b, so that the small-sized electronic components 6 a and the media 6 b are prevented from fitting into the grooves 11.

[0036] In the cathode 4 a shown in the drawing, three grooves 11 per one cathode 4 a are preferably arranged so as to be substantially parallel to each other. The number and the intervals of the grooves can be changed, if desired.

[0037] The extending direction of the grooves 11 formed in each of the four cathodes 4 a is substantially coincident with the radial direction of the component-container 7, as shown in FIG. 1. The extending direction of the grooves 11 may be optionally changed.

[0038] Moreover, each of the grooves 11 preferably has a substantially V-shaped cross-section, as shown in FIG. 2B. In addition, the groove may have a substantially U-shaped configuration, a substantially quadrangular-shaped configuration, or other suitable configuration.

[0039]FIG. 3 illustrates a second preferred embodiment of the present invention, and corresponds to FIG. 2A.

[0040] According to this preferred embodiment, a plurality of the grooves 11 are formed on the upper surface of a cathode 4 b shown in FIG. 3, and moreover, a plurality of grooves 11 a are arranged so as to intersect the grooves 11, that is, so as to be substantially perpendicular to the grooves 11.

[0041]FIGS. 4A and 4B illustrate a third preferred embodiment of the present invention, and correspond to FIGS. 2A and 2B, respectively.

[0042] A plurality of small holes 12 are formed on the upper surface of a cathode 4 c shown in FIGS. 4A and 4B. These small holes 12 form concavities. The sizes of the small holes 12 are preferably smaller than those of the small-sized electronic components 6 a and the media 6 b to be plated, so that the small-sized electronic components 6 a and the media 6 b are prevented from fitting into the small holes 12.

[0043] The number and the distribution of the small holes 12 may be optionally changed, if necessary.

[0044] The small holes 12 are preferably substantially circular in the plan view thereof as shown in FIG. 4A, and may be angular in the plan view instead of the substantially circular shape. Moreover, the grooves 11 have a substantially V-shaped configuration in the cross section as shown in FIG. 4B, and may have a substantially U-shaped configuration, a substantially quadrangular shape, or other suitable shape.

[0045]FIGS. 5A and 5B illustrate a fourth preferred embodiment of the present invention, and correspond to FIG. 2A and 2B, respectively.

[0046] In the case of a cathode 4d shown in FIG. 5B, a chamfer portion 13 is provided on the circumferential edge of the upper surface of the cathode 4d. The chamfer portion 13 defines a concavity. The size of the concavity defined by the chamfer portion 13 is preferably smaller compared to the sizes of the small-sized electronic components 6 a and the media 6 b to be plated, so that the small-sized electronic components 6 a and the media 6 b are prevented from fitting into the concavity.

[0047] The chamfer portion 13 shown in the drawing is bent to a radius as shown in FIG. 5B, and may be changed to be an inclined flat surface.

[0048] According to the above-described first to fourth preferred embodiments, the region of a cathode to which an electric field is readily concentrated during plating can be divided and distributed in the vicinities of the grooves 11, those of the grooves 11 and 11 a, and those of the small holes 12, and in the vicinity of the chamfer portion 13. Thus, the electric field, which would be concentrated, can be dispersed. Accordingly, the phenomenon in which a relatively large amount of deposit 9 is formed only on the edge of the cathode 4, so that a protuberance 10 is formed, as shown in FIG. 7, is prevented from occurring. Thus, formation of the protuberance 10, which would disturb the agitation of the small-sized electronic components 6 a and the media 6 b, can be prevented from occurring.

[0049] Moreover, according to the first to fourth preferred embodiments, the grooves 11 and 11 a, the small holes 12, and the chamfered portion 13 are formed as the concavities so as to have such sizes that the plating-pieces 6 such as the small-sized electronic components 6 a and the media 6 b are prevented from fitting into the concavities. This is done to prevent the small-sized electronic components 6 a and the media 6 b from fitting into the concavities and disturb the agitation thereof.

[0050] If the concavities have sizes that are sufficiently larger than those of the small-sized electronic components and the media, the components and the media, even if they are fitted into the cavities, can be easily moved out of the concavities. Thus, they are prevented from staying in the concavities, and the agitation thereof is not disturbed.

[0051] Hereinafter, experimental examples carried out to identify the advantages of preferred embodiments of the present invention will be described.

[0052] In an experimental example, which is an example of preferred embodiments of the present invention, the component container 7 having an inner diameter of about 25 cm, having the four cathodes 4 a arranged therein, as shown in FIG. 1, was disposed in the plating apparatus 1 as shown in FIG. 6.

[0053] Also in this experimental example, as the cathode 4 a, two types of cathodes having diameters of about 20 mm and about 30 mm were disposed in the component containers 7, respectively.

[0054] Three grooves 11 were formed at intervals of about 5 mm on each of the above-described cathodes 4 a having a diameter of about 20 mm. For each groove, the width was about 0.3 mm, and the depth was about 0.2 mm.

[0055] Regarding the respective cathodes 4 a having a diameter of about 30 mm, three grooves 11 were formed at intervals of about 5 mm. For each groove 11, the width was about 0.3 mm, and the depth was about 0.2 mm.

[0056] As the small-sized electronic components 6 a to be plated, monolithic capacitors each having approximate dimensions of 1.0 mm×0.5 mm×0.5 mm were used. The surfaces of outer electrodes disposed on both end surfaces of each monolithic capacitor were plated.

[0057] On the other hand, as a Comparative Example, plating was carried out under the same conditions as those used in the above-described example of preferred embodiments of the present invention, except that a cathode having no grooves formed thereon was used.

[0058] The following Table 1 shows the maximum thicknesses of deposits formed on the cathodes in the example of preferred embodiments of the present invention and Comparative Example, respectively. TABLE 1 Diameter of Comparative cathode Example example 20 mm   3 mm 8 mm 30 mm 1.5 mm 5 mm

[0059] As seen in Table 1, for the cathodes having diameters of about 20 mm and about 30 mm, the maximum thicknesses of a deposit portion in the example of preferred embodiments of the present invention are smaller than those in the Comparative Example. Accordingly, it is estimated that formation of protuberances on the deposit was prevented in the example of preferred embodiments of the present invention.

[0060] Table 2 shows peeling or not of deposits on the cathodes and the thicknesses (average) of plated-films formed on the outer electrodes of the monolithic capacitors in the example of preferred embodiments of the present invention and the Comparative Example for the cathodes each having a diameter of about 20 mm, respectively. TABLE 2 Plating thickness Peeling of deposit (average) Example peeling 4.9 μm Comparative not peeling 3.4 μm example

[0061] As seen in Table 2, according to the example of preferred embodiments of the present invention, peeling of a deposit on the cathode is reliably prevented.

[0062] Moreover, the plating thicknesses were compared. The thickness could be increased in the example of preferred embodiments of the present invention, compared to that in the Comparative Example.

[0063] As seen in the results of the plating-film thickness shown in Table 2 and those of the maximum thickness of deposits on the cathode shown in Table 1, the maximum thicknesses of deposits on the cathodes in the example of preferred embodiments of the present invention are smaller that those in the Comparative Example. Thus, the following is estimated. Formation of protuberances, which would disturb the agitation of the monolithic capacitors to be plated, is reliably prevented, so that the monolithic capacitors could come into contact with the cathode more fluently. As a result, the plating films each having a large thickness could be obtained.

[0064] In the above-described experimental examples, the three grooves 11 extending substantially parallel to each other were formed on the cathode 4 a with a diameter of about 20 mm as in the example of preferred embodiments of the present invention as shown in FIGS. 1, 2A, and 2B. It was determined that when the cathode 4 b having the three grooves 11 extending in the longitudinal direction and the three grooves 11 a extending in the lateral direction is used, the maximum thickness of a deposit on the cathode 4 b can be further reduced by about 2 mm.

[0065] As described above, according to preferred embodiments of the present invention, the concavities are formed on the surface of the cathode which is to come into contact with the small-sized plating pieces. Therefore, during plating, an electric field is readily concentrated in the vicinities of the concavities in addition to the edge of the cathode. Thus, the phenomena in which a larger amount of deposits are concentrated on the edge of the cathode, which causes protuberances or the like to be formed on the deposits, are reliably prevented.

[0066] Accordingly, disturbance of the agitation of the small-sized plating-pieces, which would be caused by the protuberances or the like, can be eliminated. Thus, the efficiency of plating is greatly improved.

[0067] Moreover, the concavities have anchor-effects on a deposit formed on the cathode and prevent the deposit from peeling off from the cathode. Therefore, the deposit as foreign matters is prevented from adhering to the small-sized plating pieces. Moreover, the size of the cathode can be increased without any problems. Thus, the amount of deposit per unit area of the cathode can be increased, and also, the efficiency of plating can be greatly improved.

[0068] Especially, when the above-described concavities are a plurality of the grooves formed on the surface of the cathode which is to come into contact with the small-sized plating-pieces, the concavities can be easily distributed completely on the surface of the cathode. Thus, an electric field generated during plating can be dispersed more effectively.

[0069] The above-described effects can be surprisingly achieved when a plurality of the grooves are formed so as to intersect each other.

[0070] According to preferred embodiments of the present invention, preferably, the apparatus further includes a container for components which can accommodate a plurality of the small-sized plating pieces in a plating solution, and the cathode is arranged so as to form a portion of the bottom of the container. In this case, the present invention can be applied most advantageously. In particular, according to this constitution, when the container is rotated about a vertical axis thereof, agitation-action is applied to the small-sized plating-pieces. In this state, the agitation-action can be more effectively exerted to the small-sized plating-pieces.

[0071] While preferred embodiments of the invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the invention. The scope of the invention, therefore, is to be determined solely by the following claims. 

What is claimed is:
 1. An apparatus for plating a plurality of small-sized plating-pieces comprising: a plating bath in which a plating solution is provided; and a cathode and an,anode made of conductors, which are dipped into the plating solution, respectively, the cathode having at least one concavity formed on a surface thereof which is to contact with the small-sized plating-pieces; wherein a plurality of the small-sized plating-pieces are caused to contact with the cathode in the plating solution, and conduction is carried out between the cathode and the anode, so that plating films are deposited onto the small-sized plating-pieces.
 2. An apparatus for plating small-sized plating-pieces according to claim 1, wherein the at least one concavity includes a plurality of grooves formed on the surface of the cathode.
 3. An apparatus for plating small-sized plating-pieces according to claim 2, wherein the plurality of grooves are arranged so as to intersect each other.
 4. An apparatus for plating small-sized plating-pieces according to claim 1, wherein the at least one concavity includes a plurality of small holes formed on the surface of the cathode.
 5. An apparatus for plating small-sized plating-pieces according to claim 1, wherein the concavity includes a chamfer portion formed on the circumferential edge of the surface of the cathode.
 6. An apparatus for plating small-sized plating-pieces according to claim 1, further comprising a container which contains a plurality of the small-sized plating-pieces in the plating solution, and the cathode is arranged so as to define a portion of the bottom of the container.
 7. An apparatus for plating small-sized plating-pieces according to claim 6, wherein the container is rotatable about a vertical axis of the container.
 8. An apparatus for plating small-sized plating-pieces according to claim 1, wherein the small-sized plating pieces include small-sized electronic components.
 9. An apparatus for plating small-sized plating-pieces according to claim 7, further comprising a shaft, wherein the container is rotatable about the shaft and four electrodes are arranged at intervals of about 90° around the shaft.
 10. An apparatus for plating small-sized plating-pieces according to claim 2, wherein widths of the grooves are smaller than the sizes of the small-sized electronic components.
 11. An apparatus for plating small-sized plating-pieces according to claim 2, wherein each of the grooves has one of a substantially V-shaped cross-section, a substantially U-shaped configuration, and a substantially quadrangular-shaped configuration.
 12. An apparatus for plating small-sized plating-pieces according to claim 4, wherein diameters of the holes are smaller than the sizes of the small-sized electronic components.
 13. An apparatus for plating small-sized plating-pieces according to claim 4, wherein each of the holes has one of a substantially V-shaped cross-section, a substantially U-shaped configuration, and a substantially quadrangular-shaped configuration.
 14. A method of plating a plurality of small-sized plating-pieces comprising the steps of: providing a plating bath in which a plating solution is provided; providing a cathode and an anode made of conductors, the cathode having at least one concavity formed on a surface thereof which is to contact with the small-sized plating-pieces; dipping the cathode and the anode into the plating bath so as that a plurality of the small-sized plating-pieces are caused to contact with the cathode in the plating solution, and conduction is carried out between the cathode and the anode, so that plating films are deposited onto the small-sized plating-pieces.
 15. The method according to claim 14, wherein the at least one concavity includes a plurality of grooves formed on the surface of the cathode.
 16. The method according to claim 15, wherein the plurality of grooves are arranged so as to intersect each other.
 17. The method according to claim 14, wherein the at least one concavity includes a plurality of small holes formed on the surface of the cathode.
 18. The method according to claim 14, wherein the concavity includes a chamfer portion formed on the circumferential edge of the surface of the cathode.
 19. The method according to claim 1, further comprising the step of rotating the container about a vertical axis of the container during depositing of the plating films onto the small-sized plating pieces.
 20. The method according to claim 15, wherein widths of the grooves are smaller than the sizes of the small-sized electronic components.
 21. The method according to claim 15, wherein each of the grooves has one of a substantially V-shaped cross-section, a substantially U-shaped configuration, and a substantially quadrangular-shaped configuration.
 22. The method according to claim 17, wherein diameters of the holes are smaller than the sizes of the small-sized electronic components.
 23. The method according to claim 17, wherein each of the holes has one of a substantially V-shaped cross-section, a substantially U-shaped configuration, and a substantially quadrangular-shaped configuration. 